1. Field of the Invention
The present invention relates generally to drilling devices, and, particularly, relates to drilling devices for providing increased anchorage, and, in greater particularly, relates to drilling devices for providing a conical anchorage cavity in a bore hole.
2. Description of the Prior Art
The need for anchoring objects to other surfaces is well known. The material of the substrate may be plastic, wood, bone, concrete, metal, for example, and thus require any anchoring system that is acceptable to many materials. Some materials are brittle and are not able to be threaded by a tap such as concrete and thus the bore hole must be otherwise modified to hold an anchoring system. An anchor bolt may be glued into the bore hole, but this may not be sufficient to hold significant loads under stressful conditions and quickly result in catastrophic failure. The use of anchor bolts with expanding walls is also well known, but again, under stressful conditions such as high vibrations even these may result in loosening of the anchor and eventual failure. A more positive solution to this problem is the modification of the bore hole by undercutting the wall.
This problem is addressed in prior patents. For example, one patent discloses an internal cam shaft for rotating a cutting blade into the substrate to produce an undercut portion. Another embodiment shows an expanding balloon held by an internal shaft to push out a pivoted blade. These require modifications to the drill. Another embodiment shows a cantilevered cutting blade which deploys upon a change in the rotation of the drill. There is no external control over the cutting blade itself and further there is no way of removing debris that is created when rotating the drill counter to its normal flute direction which may result in clogging of the cutting blade, breaking of the cutting blade and jamming of the drill in the hole upon an attempted removal. Another patent discloses a drill bit having means for undercutting being extendable fingers running along the shank of the drill. A guide sleeve mounted to the shank operates to extend the fingers when coming into contact with the surface of the workpiece. The number of moving parts would thus expose this drill bit to jamming considering its use in concrete undercutting for example.
Several patents disclose undercutting drill bits having fixed lateral cutting blades. One type requires that the drill shank be rocked laterally to cause the enlargement of the hole and another discloses the undercutting head being smaller than the diameter of the actual bore hole. These are specialized undercutting tools without the traditional drill bit for making of the bore hole thus requiring multiple insertions and removals to achieve an anchor cavity. Other patents disclosure undercutting bits having blades that are deployable by means of spring biased shafts.
Accordingly, there is an established need for a combined drilling device having cutting blades for undercutting, flutes for removing debris, and a minimum of moving parts that provides these features.